【作者】 李双应；

【导师】 岳书仓；

【作者基本信息】 合肥工业大学 ， 矿物学、岩石学、矿床学， 2004， 博士

【摘要】 以现代沉积学和大陆动力学理论为指导，结合岩石学、地球化学、同位素年代学等诸多学科，对大别山造山带北缘地区中生代地层进行沉积学、盆地分析以及构造演化研究。主要研究内容包括：①厘定大别山北缘地区中生代地层的年代格架；②划分岩相，确立沉积体系；③确定中生代盆地古流向，恢复盆地的古地理；④确定物源区物质组成、演绎物源区原始构造层序、建立盆地沉积物与物源区地质单元的耦合关系；⑤根据沉积学以及区域地质研究，重塑大别山中生代构造演化历史，探讨大别山造山带的碰撞成因机制。本文取得了如下成果和认识。 1．在周公山组中在凤凰台组中发现了火山凝灰岩层利火山岩碎屑，结合同位素年代学研究以及沉积相和重矿物对比，重新厘定了大别造山带北缘中生代地层的格架。为研究区沉积体系、造山带演化、折返年代学以及山盆耦合关系研究等奠定了基础。 2．根据岩相、相组合以及沉积层序的研究，确立了研究区的沉积作用类型和沉积体系，它们包括碎屑流和超浓缩洪流沉积、辫状河河道沉积，以及冲积扇沉积、洪泛平原沉积、扇三角洲沉积和湖相浊流沉积。在此基础上，建立了盆地的沉积体系格架。 3．通过古水流研究，恢复了大别造山带北缘中生代的古地理。沉积盆地的水系可以分为两类，一是靠近南缘的横向水系，它们主要是从南向北，另一类是靠近盆地中部的纵向水系，它们是从西向东。物源区主要位于南部，为大别造山带。 4．首次在毛坦厂组、凤凰台组中发现了榴辉岩砾石，这一发现表明大别造山带超高压变质岩在早白垩世已经折返到地表，而且地球化学研究表明这些榴辉岩砾石的原岩形成于岩浆岛弧构造背景。 5．物源分析表明，位于肥西地区中生代碎屑岩主要来自佛子岭群和卢镇关群变质岩，凤凰台组的源区来自于一个已经消失的以岛弧榴辉岩为代表的含超高压变质岩单元。大别杂岩在新第三纪已经遭受剥蚀，构成了正阳关组的物源。同时也揭示了大别造山带的折返剥露历史，大别造山带在早侏罗世(205-180Ma)之前快速抬升，侏罗纪经历了相对平静阶段。侏罗纪末(135Ma)到早白垩世源区产生剧烈的持续上升和剥蚀，早白垩世晚期，源区的构造转换为拉张。晚白垩世(95Ma)，盆地边缘与源区一道抬升，遭受剥蚀。 6．大别山北缘中生代沉积作用具有穿时特征，沉积作用开始时间自东向西依次为早中侏罗世、中晚侏罗世和早白垩世。揭示了大别山造山带的折返是穿时的，隆起自东向西进行，而其控制因素主要为NE向的断裂体系。 7．大别造山带是一个具有转换叠加性质的造山带。NE向郯庐断裂系的大型平移作用叠加在原来印支期消减带之上，产生新的俯冲。大别山造山带的构造模式是三叠纪扬子陆块的向北俯冲和侏罗纪华北陆块的向南俯冲，构成大别山造山带的对冲模式，其动力学背景是太平洋构造域对古特提斯构造域的叠加。 8．将大别山造山带的构造演化与华北、扬子陆块的演化紧密结合，提出了大别山造山带三开三合的构造演化特征，即新元古代的古岛弧发育和震旦纪的拼合、奥陶-早志留世的拉张和加里东期的拼合、二叠纪-早三叠世的拉张和印支期的拼合以及侏罗纪-新生代的折返隆升剥蚀。更多还原

【Abstract】 This research focuses on the sedimentology, basin analysis and tectonic evolution of Mesozoic strata in the north margin of the Dabie Orogenic Belt, using an integrated approach of modern sedimentology, continental dynamics, petrology, geochemistry and isotope chronology. The topics of the study include: (1). establishing the time framework of Mesozoic strata in the north margin of the Dabie Orogenic Belt; (2). analysis of lithofacies and sedimentary systems; (3). ascertaining the paleocurrent direction of the Mesozoic basin and reconstructing the paleogeography; (4). deciding the material components and original structure sequences of the basin provenance, and coupling relationship between the sediments of the basin and geologic units of the provenance; (6). establishing the Mesozoic tectonic evolution history of the Dabie Orogenic Belt and discussing the collisional mechanism of the Belt. The results are listed as follows.1.The framework of Mesozoic strata in the north margin of the Dabie Orogenic Belt was reestablished according to the discovery of the tuff beds and volcanic debris in Zhougongshan and Fenghaungtai Formations, along with their isotope ages and the correlations of sedimentary facies and heavy minerals. This result lays a solid foundation for the research.2.Based on the study of petrology facies, facies association and sedimentary sequences, the sedimentary processes and systems are established. They consist of debris and hyper concentration flow deposits, channel deposit of braided and meandering streams, and alluvial fans, floodplains, fan-deltas and lacustrine turbidities. Based on these results, the framework of sedimentary system in the study area is established.3.The Mesozoic paleogeography of the north margin of the Dabie Orogenic Belt was established according to the paleocurrent study. Water system of the sedimentary basin is divided into two classes: one is transverse water system adjacent to the south margin of the basin , which flows from the south to the north, the other is longitudinal water system close to the midst and flows front the west to the east. The provenance of the basin is located in the south, which covers the Dabie Orogenic Belt.4.It is the first time that eclogite conglomerates are discovered in Maotangchan and Fenghuangtai Formations. This suggests that ultra-high pressure metamorphic rocks in the Dabie Orogenic Belt exhumed to the earth’s surface in Lower Cretaceous. The geochemistry data indicates that the protoliths of the eclogite gravels formed in a structure setting of volcanic arc.5.Based on the analysis of their source rocks, the Mesozoic detrital rocks in Feixi area are mainly derived from metamorphic rocks of Fuziling and Luzhengguan Groups, and the provenance of Fenghuangtai Formation is a disappeared ultra-high pressure metamorphic rock unit characterized with inland arc eclogites. The Dabie complex suffered denudation in Neogene and constitutes the source rocks of Zhengyangguan Formation. These facts indicate that the Dabie Orogenic Belt was uplifted rapidly before the early Jurassic (205-180Ma), and went through a long period of tectonic calm during the Jurassic. At the late stage of Upper Jurassic (135ma), the provenance areas underwent intense and sustained uplift and denudation. In the period of Lower Cretaceous, the tectonic setting of the provenance areas turned into strike-slip. In the Later Cretaceous (95Ma), the provenanceareas and the margin of the basin uplifted and suffered denudation together.6.The Mesozoic sedimentation in the north margin of the Dabie Orogenic Belt is diachronous. From east to west, the onset of the sedimentation is successively in Lower-Middle Jurassic, Middle-Later Jurassic and Lower Cretaceous. This indicates that the exhumation of the Dabie Orogenic Belt was diachronous, and that its uplift happened from east to west and was mainly controlled by the NE fault system.7.The Dabie Orogenic Belt is of transformation and superposition character. Its new superimpose更多还原